This invention relates to a device for adjusting chain length to accomodate different lifting points of chains used either as tie downs or more particularly as chain slings for lifting and moving heavy industrial equipment and materials.
There are many applications in industry where it is necessary to lift and/or transport heavy industrial materials such as machinery, automobiles or coils of rolled steel. To do this, many rigging crews will employ link chains for the slings and tie down systems which are needed. However, the expense and weight of chain based devices are such that most rigging crews will carry only a few, relatively long chains, to meet their needs. On most occasions, however, it is seldom that they will have a chain that is precisely the right length for the application at hand. In most cases the chain will be too long and it is necessary to adjust the chain length to meet the particular needs without compromising either its ability to meet that need or its utility for other applications where the full length of the chain might be necessary. Many times this adjustment is accomplished by the use of a grab link of some type. In other applications the chain is passed either around or through a loop or shackle attached to the particular item being transported with the free end then being clamped with a grab hook or similar device to one or more of the links along the working length of the sling. In still other cases, various devices have been developed which allow shortening of the chain in the middle thereof leaving both ends free to be attached to a support such as the hook of a crane on one end and to the object being lifted on the other. However, one problem with many of these devices is their complexity and attendant high cost which results from the many welds and the relatively large amount of labor required for their manufacture.
A second problem is often encountered when the chain either has no end pieces or has end pieces of the wrong type - such as a grab hook when a master ring is needed for crane attachment. In such cases it is often necessary to rig up some sort of connection device and attach it, in some way or other to the chain so it can be used.
In practically all of these cases, however, it has been found that such techniques eventually cause severe deterioration of the ability of the chain to handle its full load capability. This may occur, on one hand, by cracking of the chain links due to localized high stresses induced by the method of clamping, or by overstraining the particular links causing them to become brittle through work hardening. In still other cases they induce severe bending movements which act to twist, distort or stretch the links beyond their yield point thus causing failure. A technique or device is required which will allow an adjustment of the length of a chain to meet varying industrial applications without affecting its ability to handle loads when fully extended and without shortening its expected service life.